Chair back



FIG. 1 is a rear perspective view of our new design;

FIG. 2 is a detailed perspective view thereof;

FIG. 3 is a left side view thereof, the right side being a mirror image thereof;

FIG. 4 is a detailed left side view thereof; and,

FIG. 5 is a rear view thereof.

The views of the chair back not shown form no part of the claimed design. The dash-dash lines in the figures show portions and features that form no part of the claimed design. The dash-dot lines in the figures represent the unclaimed boundary of the design. 

CLAIM We claim the ornamental design for a chair back, as shown and described. 